Seal for vacuum apparatus.



F. e. KEYES. SEAL FOR VACUUM APPARATUS. APPLICATION FILED HAH. 6. 1913.

l; 55993559 Patened Nov. 2, 1915.

UNITED sTATEs PATENT oEEioE- FREDERICK G. KEYES, BOSTON, MASSACHUSETTS, ASSIGNOR TO ARTHUR A. NOYES, TRUSTEE, 0F BOSTON, -MASSACHUSETTS.

SEAL FOR VACUUM APPARATUS.

Application filed March 6 I 1913.

To all whom t may concern: y

Be it known that I, FREDERICK G. KEYES, a citizen of the United States, and iesident of Boston, in the county of Suffolk and State of Massachusetts,'have invented new and useful Improvements in Seals for Vacuum Apparatus, of which the following is a specification.

My invention relates to improvements in seals for vapor electric apparatus, and is more particularly addressed to the construction of hermeticv seals for introducing an electric current into a vapor electric appay ratus and which shall be permanent and reliable during the operation of the apparatus at elevated as well as at ordinary temperatures.

My invention is well illustrated in connection with arc lamps of the mercury vapor type. I Such lamps possess a high efficiency and are well adapted to many commercial purposes, for illumination as well as others. It has been found that by inclosing the arc in a chamber of highlyresistant material, such as fused silica, the efficiency and general adaptability of the lamp is greatly increased.V Much difficulty has hitherto been experienced in the introduction of leads into containers constructed of fused silica. In commercial practice conical plugs of nickel steel are ground into a heavy tube of fused silica, and these plugs are further tightened by means of liquid mercury. Such seals, however, have proved very unsatisfactory in practice. Recently, in a copending application by C. A. Kraus, Serial No.. 688,815, filed April 5, 1912, a hermetic seal has been developedwhich is adapted to fused silica containers, and which possesses many advantages oi er seals hitherto constructed. This seal consist of a tubular metal member, such as platinum, which is sealed through a fusible glass of much lower coetlicient of expansion than that of the metal tube. When a container of fused silica is employed,I the glass, through which the metal tube is sealed, has a coefficient of expansion practically the same as that of fused silica, i. e. a coefficient so low that under very severe treatment, as for instance, quenching in water, the liunction between the glass and the fused silica retains its integrity. These seals are very useful for manifold purposes, but inthe case of certain mercury vapor arc lamps, the metal Specification of Letters Patent.

Patented Nov. 2, 1915.

Serial No. 752,316.

cury4 to alloyV with the metal tube, as platinuin for example, is very greatly increased. If such alloying takes place, the metal of which the tube is constructed loses its ductility and plasticity which is an essential feature of the seal in question. For, since the metal tube has a higher coefficient of thermal expansion than the surrounding glass, it is in a state of tension and this state is of great utility so long as it can be maintained under conditions wherein the superiicial adhesive force between the glass and the metal is sufficiently great to overcome the tensile stress in the metal tube itself. To insure these conditions, avery soft or ductile metal such as platinum is employed. When, however, at high temperatures, the mercury alloys with the metal, the said metal loses its necessary condition of plasticity and ductility, the necessary stress conditions as between the glass and the metal tube are no longer fulfilled and the seal loses its hermetic vacuum tight quality.

My invention is addressed to providing means for preventing the liquid metal or metal vapor, as for example mercury, from coming into contact andv alloying with the metal tube, for if the alloying of the `Imercury with the metal tube can be prevented, the metal tube will retain its original condition of ductility and plasticity and the seal will retain its hermetic and vacuum tight qualities.

My invention will be better understood in connection 4with the accompanying iigures which illustrate the method of practising the same, and in which:

Figure 1 represents a longitudinal section of a seal embodying myy invention; Fig. 2 represents a sectional view of another seal embodying my invention but differing from Fig. 1 is specific detail; Fig. 3 represents a sectional view of another seal embodying my invention but differing from the preceding seals in specific details; Fig. 4 represents a section of still another seal embodying my invention with certain variation of specific detail; and Fig. 5 represents a section of still another seal embodying my invention with variation as to specific detail.

in this specific instance assume to be platinum. C is constructed. of vitreous material possessing a coeiicient of expansion less than .the platinum tube B vided with a lead F.

v joined to the container into which it is de' current.. This container that of the metal member B, and approaching that of. the vitreous member A very closely.. "When the member A is constructed of fused silica and the member B of platinum, asI have assumed for the sake'of illustration, I recommend that the member C be constructed of a composition comprising silica A.(,SiC2) yand boric acid (B203) in its essentialelements.; This composition of matter has'` been fully described by Keyes and Kraus in a .co-pending application, Se-

rial No; 752,34, filed concurrentlywith the present application. rIhe material of which the member C is constructed as described above, possesses a melting point sufficiently low so that it may be applied and-sealed to melting the same. At the same time the adhesive forces between the tubular memL ber B and the surrounding vitreous member C are such that no forces can arise in the tubular member itself which are able to overcome the intimacy of contact between the contiguous surfaces of B and C, and the permanent integrity of -th`e juncture between the two members is thus assured. The member C is in turn sealed to tube A at the point D. The coelicient of expansion of the member C must approach that of the member A suiiciently closely to render the juncture at D asecure and permanent one. If the container material A has a suficiently low melting point, it may be sealed directly to B and C maybe omitted. For most purposes it is preferable that the tubular metallic member B should be provided with a metallic lead F attached to the outer end of the tube B and passing through B, in which case the tube B does not, itself act in carrying the current. In some cases, however, it is suiiicient to employ 4the tnbe B itself as a conductor for introducing the current as shown in Fig. 2, the inner end of the platinum tube B being closed and pro- 'Ihe end of the lead F is joined to the end of the tube B. by fusion or by soldering. The end of the tube A is sired to introduce comprises aquantity ofpmore or less volatile metal, such as mercury, through the vapor of which the arc passes. The tube A- is therefore eitherfilled with metal or metal vapor. As lalreadv set forth, this metal tendsl to alloy with the metallic tube B, particularly when, as in the quartz mercury arc without danger of lamp, the apparatus is operated at elevated temperatures.

I have found, and this constitutes an 1mportant element inmy invention, that by 1ntroducing a suitable means to prevent or hinder the fiow or diffusion of the-metal or the metal vapor into the neighborhood of the tube B, this deleterious alloying may be prevented or so hindered that a seal of this type may be employed in operating quartz mercury arc lamps for extended periods of time without visible or detectable impair'- ment of the seal.

It is to be understood that the term quartz as employed in connection with a vapor electric lamp signilies fused silica, a product which is obtained either by fusing crystalline silica (SiO), which is quartz proper, or silica in some other form which is not crystalline.` -As I employ the term -in the specified connection, quartz is synonymous with fused silica.-

To prevent the action of mercury on the tube B, I interposerabarrier material'G. Since fusedE silical as well as the glass of which the member C is constructed both have very low coeiicients of expansion while the tube B and the leaf F have much larger coefficients of thermal expansion, it is necessary that the barrier G shall be constructed of a material which shall at all temperaturesv adapt itself and conform to the shape and dimensions of the different members A, C, B and F To obtain this adaptability, in view of thel fact that the different members possess greatly varying coeffioients ,of expansion, the barrier material to put any part under undue stress while -at the same time forming| contact with all.

Throughout the specification and claims I shall employ the term yielding quality,to designate the above described characteristic of the barrier material and to the barrier as a barrier of.yielding' material. As bar-A rier material I employ various materials such as semiplastic resin, either natural or artificial which at high temperatures pos- Sess just enough plasticity to yield to the volume changes imposed by thermal change of the various parts; a loosely fritted material, the minute particles of which adjust themselves as the temperature changes; or, What I prefer in mostcases, a pulverulent material, such 'as ferric oxid, the interstices between the particles of which are so minute that-even mercury vapor penetrates with eX- treme difficulty andslowness. i

When a pulverulent material is employed as barrier, I retain itin its desired position by means of a suitable diaphragm. A seal so provided is shown in Fig. 3. Here, as in all the figures, corresponding letters are employed for `corresponding parts. G is the barrier constructed of pulverulent material las lead F and is contained within the tube A and sealing member C. To confine the material (lr to its proper place a diaphragm H is provided through which the lead F passes. The opening in H through which the lead passes is preferably made slightly larger than the lead so that it is not engaged thereb y but slips freely. By this means the difference in expansion between F and A is provided for and no stress results on the seal itself owing to this cause.

Another variation of my invention is illustrated in Fig. 4. Here the diaphragm I-I engages a tubular metallic member I within which the lead F slides making contact therewith. rIhe diaphragm may be constructed of a material that is introduced in the form of a powder or paste which is later baked into a more or less coherent mass. In some cases also, as shown in Fig. 5, the entire diaphragm I may be constructed of metal. The edge of the diaphragm in this case is preferably made thin so that it will not unduly stress the tube A. The tube A is further provided with an annular groove J which engages the edge of the diaphragm I.

That I claim and desire to secure by Letters Patent is:

'1. In .a vapor electric apparatus, a container constructed of non-conducting material, a metallic member sealed through the wall of the container, a barrier of yielding material interposed between the metallic member and the interior ofthe container for the purpose of intercepting the vapor or its liuuid in order to protect the metallic Vmember against deterioration.

2. In a vapor electric apparatus containing a vaporizable liquid, a seal comprising a tubular'metallic member sealed through a vitreous envelop of lower coefficient of thermal expansion than that of the metallic tube, and means to intercept the vapor or liquid in order to prevent the deterioration of themetal tube thereby.

3. In a vapor electric apparatus containing a vaporizing fluid, a seal comprising a tubular metallic member sealed through a vitreous member of lower coeiiicient of expansion than that'of the tubular member, a barrier of yielding material interposed between the vapor or liquid and the tubular member to protect the said member against detei'ioration by the vapor or liquid.

l. Inl a vapor electric apparatus containing a vaporizable liquid, a seal comprising a tubular metallic member sealed through a vitreous member of lower coeificient of eX- pansion than that of the tubular member, a lead extending into the interior. of the vapor electric apparatus and a barrier of yielding material interposed between the liquid or its vapor and the tubular memberl and engaging the lead.

5. In a vapor electric apparatus comprising a metallic vapor, a container of nonconducting material, a tubular metallic member of higher coetlicient 0f expansion than that of the container material, and sealed through the container wall, a barrier of yielding material interposed between the tubular metal member and the vapor or its l liquid within the container to prevent the deterioration of the tubular member.

6. In a vapor electric apparatus, a container of fused silica and containing mercury, a metallic tube sealed through the walls of the container, a barrier of yielding material interposed Abetween the interior of the container and the metallic tube to protec-t the tube against the action of mercury.

7. In a vapor electric apparatus, a container constructed of fused silica, and containing mercury, a platinum tube sealed through the wall of the container, a barrier of yielding material interposed between the interior 'of the container and the .platinum tube' to protect the tube against the action of mercury.

Signed by me at Boston,Massachusetts this twenty fifth day of February, 1913.

FREDERICK G. KEYES.

IVitnesses:

` ODI'N ROBERTS,

FLORENCE A. COLLINS. 

